The present invention relates to perovskite-type oxide films, production processes and evaluation methods for such films, as well as devices using such films.
In recent years, research and development have been conducted actively on a variety of devices such as actuators, sensors and memory devices for which piezoelectric materials are used, whereupon piezoelectric films deposited by a vapor-phase deposition technique such as sputtering receive attention as high-performance, functional films. The piezoelectric films are used as a piezoelectric thin-film device for a piezoelectric actuator in an inkjet recording head (liquid ejecting device), a micropump, and so forth, of which a high piezoelectric performance is required.
At present, the piezoelectric thin-film device is decreased in displacing capability upon application of an electric field thereto, that is to say, deteriorated, as it is exposed to a higher relative humidity and temperature.
Specifically, a problem lies in that the moisture around a piezoelectric film increases a leakage current to cause dielectric breakdown or promotes ion migration by making a constituent of the piezoelectric film ionized.
Measures against heat and humidity are accordingly critical to the piezoelectric films of which a high piezoelectric performance is required, and also indispensable from the viewpoint of the durability of a device using a piezoelectric film.
For the purpose of increasing device durability, US 2006/0046319 A1, for instance, proposes distribution of the mean stress received by a piezoelectric film by providing a stress-relieving layer which is formed by orientational film deposition or epitaxial film deposition.
In JP 2005-253274 A, it is disclosed that a stress-relieving section for relieving the stress on a piezoelectric device is provided by cutting a slit in an electrode layer.
Such a stress-relieving layer or stress-relieving section as described in US 2006/0046319 A1 or JP 2005-253274 A, however, will be provided at the expense of much time and effort, and increase the fabrication costs.
Moreover, it is not possible with the conventional measures to fully relieve the stress generated in a piezoelectric film during the application of a voltage thereto so as to attain a satisfactory device durability. One reason for this is that, while deterioration is liable to begin where stress is localized, a localized stress cannot be removed by providing the stress-relieving layer or stress-relieving section.